Method for connecting electronic components to a substrate, and a method for checking such a connection

ABSTRACT

A method for connecting an electronic components to a carrier substrate is described. At least one pad of the component is connected electrically conductively to at least one pad on an upper surface of the carrier substrate. A solder bump is deposited on at least one of the pads to be connected, the component is alignedly mated with the carrier substrate, and the at least one solder bump is soldered in order to wet the contact surfaces. 
     It is provided that during the soldering, the at least one solder bump is deformed within the contacting plane in such a way as to achieve a degree of deformation that permits the two-dimensional analysis of said degree of deformation by a radiograph of the interconnection site.

FIELD OF THE INVENTION

The present invention relates to a method for connecting electroniccomponents to a carrier substrate an arrangement for connectingelectronic components to a carrier substrate and a method for examininga connection between electronic components and a carrier substrate.

BACKGROUND INFORMATION

In is conventional to equip a carrier substrate with electroniccomponents in a flip-chip process or ball grid array (BGA) process. Inthese methods, the electronic components are provided on theirconnection side with a plurality of solder “bumps” or “balls” and arethen placed, connection side down, on a carrier substrate provided withcontact surfaces mating is being effected in that the contact surfaces,or “pads,” corresponding to solder bumps are alignedly assigned. Thesolder bumps used in the flip-chip process are usually about 75 to 80 μmin diameter and those used in the BGA process are usually about 500 to700 μm in diameter. The carrier substrate is, for example, a ceramicsubstrate, a printed circuit board, a silicon substrate or the like. Thesolder bumps are then soldered to the pads of the carrier substrate in areflow soldering process in which the solder bumps are melted in areflow furnace and wet the contact surfaces of the carrier substrate.

Such a method is described, for example, in PCT application No. WO98/14995, U.S. Pat. No. 5,284,796 and U.S. Pat. No. 5,246,880. Duringthe flip-chip process, a plurality of electrically conductiveconnections that corresponds to the number of pads to be contacted aremade simultaneously between the pads of the electronic component and thecarrier substrate.

Because of the arrangement of the connecting contacts that are producedbetween the electronic component and the carrier substrate during reflowsoldering, visual inspection is impossible. To be able to perform aninspection of the connecting contacts, in particular to check to makesure that the melted solder bumps have wet the contact,:surfaces of thepads on the carrier substrate, it is conventional to subject the bondingarrangement, consisting of the electronic component and the carriersubstrate, to x-radiation and to analyze a prepared radiograph.Depending on the material used for the solder bumps, it is possible toachieve contrast visualization on the radiograph that show the solderbumps and the regions of the composite surrounding them. Depending onthe resolution of the x-ray apparatus used, missing solder bumps orbridging between adjacent solder joints can readily be detected by thismeans. However, nonexistent or only partial wetting by the solder bumpsof the contact surfaces of the pads on the carrier substrate, forexample due to contamination of the pads, is not possible. Theseso-called “cold solder joints” hinder or prevent the operation of theelectronic components, and it is therefore imperative that they bedetected in a quality check.

SUMMARY OF THE INVENTION

The method according to the present invention offers the advantage thatnondestructive examination of electrically conductive connections madeby a flip-chip or BGA technique can be performed in a simple manner. Dueto the fact that at least one solder bump is deformed in the bondingplane during soldering to achieve a degree of deformation that permitsthe analysis of said degree of deformation by a radiograph of theconnection site, not only the presence of a solder joint, but also itsproper wetting of the pad to be contacted can be checked via theintensity variation of the x-radiation passing through the bondingarrangement or by a two-dimensional or three-dimensional radiograph ofthe connection site.

In an advantageous embodiment of the present invention, particularly foruse with the flip-chip technique, the solder bumps undergo adistribution of their material during the soldering, such that theirthickness decreases continuously toward the margin, the distribution ofmaterial, for example is determined by a solder stop mask thatencompasses the pads of the carrier substrate. It is therebyadvantageously achieved that, the initial size,and thus the initial massof the solder bumps being known, the solder bumps can undergo a defineddeformation within the bonding plane. Depending on the arrangement ofthe solder stop mask, this results in a distribution of material thatdecreases toward the margins of the solder bumps, so that a defineddeformation of the solder bumps takes place. On subsequent x-irradiationof the connection site, the x-rays are absorbed to different degrees bythe material of the solder bump, according to the distribution of thematerial of the solder bumps that has occurred, thus giving rise to anintensity variation in which the x-rays passing through the bondingarrangement exhibit a continuous transition from a maximum intensity toa intensity and vice-versa. This, continuous transition between theminimum intensity and the maximum intensity provides a simple means ofdetecting wetting of the contact surface of the pad. Particularly if thediameters of masking openings in the solder stop mask are selected for asolder bump diameter within defined ranges, a defined distribution ofthe material of the solder bump can be achieved during the reflowsoldering of the components on the carrier substrate. This thereforeproduces the continuous variation of the thickness of the solder bumpviewed in the bonding plane, and thus the continuous transition betweena minimum and a maximum intensity of the x-rays passing through thebonding arrangement.

The method according to the present invention for examining a connectionbetween electronic components and a carrier substrate further permits,in a simple manner and with high precision, the quality assessment ofcontact points obtained by a flip-chip process or the BGA technique.Because an influence on an intensity variation of x-rays passing throughthe bonding arrangement is analyzed in a region of transition from asoldered solder bump to the region surrounding it or on atwo-dimensional,or three-dimensional radiograph of the connection site,the solder bumps being deformed during soldering in such a way that whenthe pads are properly wetted it is possible to measure a continuoustransition in the intensity variation or a visible deformation of thesolder bump on the radiograph, defect-free or defective contact pointscan be recognized from the radiographs obtained.

Due to their deformation during soldering, the solder bumps undergo adistribution of their material in which the volume (thickness) decreasestoward their margins, causing a continuous transition in the intensityof the measured x-rays. Since x-radiation that is applied uniformlywithin the bonding plane to the bonding arrangement obtained is absorbedor transmitted differently, according to the distribution of thematerial of the solder bumps. This is what produces the intensityvariation on the radiograph. If the solder bumps are not properly wettedby the pads, the intended distribution of the material of the solderbumps does not take place, and there is, therefore, no measurablecorresponding continuous transition of the intensity distribution of thex-rays. Such unwetted or insufficiently wetted solder bumps aredistinguished by an abrupt transition of the intensity, distribution. Itcan therefore be concluded from the abrupt variation in intensity that a“cold solder joint” is present. A nondestructive and precise analysiscan be performed in this manner, particularly in the case of therelatively small solder bumps used in the flip-chip technique.

The unequivocal deformation of the kind that can be obtained inparticular with the relatively large solder bumps used in BGA techniquescan be rendered visible, and therefore made susceptible to analysis on atwo-dimensional or three-dimensional radiograph. Due to the relativelylarge volume of the solder bumps, a continuous transition of theintensity variation cannot be detected in this case. Here, thedeformation—with an abrupt transition in intensity between the solderbumps and the region surrounding them, evincing flawless wetting of thepad—is clearly recognizable on the radiograph.

In a further advantageous embodiment of the present invention, the padof the carrier substrate is encompassed by a solder stop mask theopening of which is larger than the pad. This advantageously makes itpossible for deformation of the solder bump to take place during thesoldering of the bonding arrangement so that edge faces of the pad thatextend substantially perpendicularly to the bonding plane of the bondingarrangement can be co-wetted by the material of the solder bump. Becausethe solder stop mask is spaced away from the pad, this gap can beutilized to permit deformation of the material of the solder bump withinthe gap, the edges of the pad simultaneously being wetted when properwetting occurs.

The proper wetting of the edges of the pad can be checked by anadvantageous method for examining the connection between the electroniccomponent and the carrier substrate. By the preparation and analysis ofa three-dimensional radiograph of the bonding arrangement in the regionof a layer that lies in a plane with the at least one pad of the carriersubstrate, proper wetting of the edges can be demonstrated in a simplemanner on the radiograph of the layer. Because only the layer in whichthe pads are disposed is picked out from the bonding arrangement as awhole and visualized, the presence of material deformed into the planeof the pad during the soldering, so that said material can wet theedges, can be identified by a ring-shaped pattern on the radiograph.

Moreover, in an advantageous embodiment of the present invention,wetting of the edges of the pad can be checked by a two-dimensionalradiograph of the bonding arrangement. In a two-dimensional radiograph,wetting of the edges can be detected very advantageously in that theintensity variation of the x-ray beams passing through the bondingarrangement exhibits a characteristic saddle shape, which, in a simplemanner, furnishes evidence of proper wetting of the edges.

Also, an advantageous embodiment of the present invention, thedeformation of the—essentially round—solder bump can be accomplished bydefined shaping of the pads. During the soldering, the solder bump wetsthee shaped pad and thereby essentially assumes its shape. Definedshapes for the pad are, for example, oval, triangular polygonal shapesor the like.

Wetting conforming to the shape of the pad produces a set deformation ofthe solder bump that can be detected on a two-dimensional radiograph. Ifthe shape of the solder bump matches the known shape of the pad, it canbe assumed that complete and therefore proper wetting of the pad hastaken place. If the shape of the solder bump on the radiograph matches,for example, the original shape of the solder bump, particularly a roundshape, it can be inferred from this failure of the solder bump to assumethe shape of the pad that improper wetting of the pad has taken place.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a detail of a cross section through a carrier substratewith a flip-chip component placed thereon before reflow soldering.

FIG. 2 shows a first embodiment of a bonding arrangement after reflowsoldering.

FIG. 3 shows a second embodiment of a bonding arrangement after reflowsoldering.

FIG. 4 shows a bonding arrangement according to the prior art afterreflow soldering.

FIG. 5 shows a cross-sectional schematic view of a third embodiment of abonding arrangement after reflow soldering.

FIG. 6 shows a schematic view of a three-dimensional radiograph of thebonding arrangement shown in FIG. 5.

FIG. 7 shows a schematic view of a two-dimensional radiograph.

FIG. 8 shows a plan view of a connection diagram of a printed circuitboard.

FIG. 9a shows a first embodiment of a circular shaped pad withprojecting lands.

FIG. 9b shows a second embodiment of a circular shaped pad withprojecting lands.

FIG. 9c shows a triangular shaped pad.

FIG. 9d shows a circular shaped pad with a triangular nose.

FIG. 9e shows a circular shaped pad with two triangular noses.

FIG. 9f shows a tear-drop shaped pad.

FIG. 9g shows an oval shaped pad.

FIG. 9h shows a square shaped pad.

FIG. 9i shows a circular shaped pad with a land.

FIG. 10 shows a schematic two-dimensional radiograph of a bondingarrangement.

DETAILED DESCRIPTION

FIG. 1 shows a detail of a cross section through a carrier substrate 10,which may be for example, a printed circuit board, a ceramic plate, asilicon substrate or the like. In the example shown here, the substrateis a printed circuit board, the upper surface 12 of which is to beequipped with electrical and/or electronic components 14. Deposited onthe upper surface 12 are printed circuit traces 16. Only one suchprinted circuit trace 16 is shown in FIG. 1 and the subsequent figures,although the carrier substrate 10 can obviously comprise a plurality ofprinted circuit traces 16. Printed circuit trace 16 terminates in a pad18 that forms a contact surface 20, which is used to establish anelectrical connection to the components 14.

The printed circuit trace 16 is provided to equip carrier substrate 10with flip-chip components and/or SMD (surface-mounted device)components, only a detail of component 14 being shown. A comparableconnecting technique is to produce solder connections by ball gridarrays. The term “solder bumps” is used interchangeably hereinbelow tosignify bumps, balls or the like.

At the mounting location of component 14, the upper surface 12 of thecarrier substrate is provided with a pattern of pads 18 that correspondto a pattern of pads 22 of component 14. Each pad 22 of the component 14that is to be contacted is therefore assigned a pad 18 of the carriersubstrate 10, i.e., the contacts are disposed opposite one another onthe confronting surfaces of component 14 and carrier substrate 10 beforecomponent 14 and carrier substrate 10 are interconnected.

Each pad 22 of component 14 possesses a solder bump (or ball) 24 that ismade of, or at least contains, an electrically conductive material. Thesolder bumps 24 are deposited on the pads 22 by conventional methods, sothis subject will not be treated in further detail in this description.In the flip chip technique the solder bumps have a diameter d₂ of about75 to e 80 μm, and in the BGA technique a diameter of about 500 to 700μm.

The pads 18 of substrate 10 are surrounded by a solder stop mask 26.Solders stop mask 26 has masking openings that correspond to the grid ofthe electrically conductive connections to be made between component 14and carrier substrate 10 and that are bounded by the side walls 30 ofsolder stop mask 26. Solder stop mask 26 is formed, for example, by asolder stop resist applied by screen printing.

The openings 28 are, for example, round and have a diameter d₁ that isselected to be larger than a diameter d₂ of the substantially sphericalsolder bumps 24. The ratio of the diameters d₂:d₁ is, for example,greater than 1:1.1, particularly 1:1.3 to 1:1.4.

A diagram below each of the schematic partial sectional views in FIGS. 1to 4 charts the intensity variation 32, over their spatial distribution,of the x-rays 34 passing through the arrangement. This represents theintensity variation 32 that occurs during passage through.<the,bondingplane of a bonding arrangement 36 (FIG. 2). The bonding plane iscoincident with a plane parallel to the upper surface 12 of carriersubstrate 10. In FIG. 1, this intensity variation 32 is shown merely forpurposes of explanation, it being clear that on reaching the bondingarrangement 36, the x-radiation penetrate it with varying intensity dueto the given composition of the material in the individual regions ofthe bonding arrangement 36. Particularly in the region of the solderbumps 24, the x-radiation 34 undergoes strong absorption, so that in thecharacteristic 38 reflecting the intensity variation 32, diameter d₂ ofsolder bump 24 is clearly apparent in characteristic 38 in the form ofan abrupt change in intensity 32.

FIG. 2 shows the bonding arrangement 36 after reflow soldering. For thispurpose, component 14 is placed on carrier substrate 10, the solderbumps 24 thus being placed on the contact surfaces 20. It is understoodthat all the solder bumps 24 of component 10 have the same dimensions,permitting the uniform placement of all said solder bumps 24 on thecontact surfaces 20 respectively assigned to them. The bondingarrangement 36 is then conveyed to a reflow soldering station. At thereflow soldering station, the solder of solder bumps 24 is heated andmelted. As a result, the material of the solder bumps 24 begins to flowand wets the contact surface 20. According to the size of the openings28 in solder stop mask 26, the material of solder bumps 24 flows to theside walls 30, so that contact surface 20 is completely wetted. The pads18 are made of a readily wettable material, for example nickel, copperor gold. Due to the good wettability of contact surfaces 20, the solderassumes the shape depicted in FIG. 2. The surface tension of the solderand the weight of component 14 cause component 14 to be moved towardupper surface 12 of carrier substrate 10 until, for example, thisapproaching movement is halted by spacers (not shown in the figures).

As the space between component 14 and carrier substrate 10 diminishes,the mass of the solder bumps 24 comes to be redistributed over itsthickness D. Based on the ratio of the diameters d₂ to d₁ (FIG. 1),there is a continuous transition of the thickness D of solder bump 24from its margin, which is defined by the side wall 30 of the maskingopening 28, to its center in the region of the pads 22 of component 14.A deformation of the solder bump 24 within the bonding plane thereforetakes place, the degree of deformation and thus the distribution of thematerial of solder bump 24 across the bonding plane being definable bythe ratio of the diameters d₂ to d₁.

It thus becomes possible to use x-radiation to check the connectionbetween component 14 and carrier substrate 10 for proper wetting ofsolder bump 24 on contact surface 20. In accordance with the intensityvariation 32 (again depicted) across the bonding plane, a continuoustransition between a maximum 40 and a minimum 42 of the intensity 32 ofthe x-radiation 34 can be observed on the basis of characteristic 38.This continuous transition—denoted as 44 in FIG. 2—corresponds in thiscase to the decrease in the thickness D of solder bump 24 in itssurface-adhesion extent within the bonding plane. It can therefore bedetermined in a simple manner, by nondestructive examination of thefinished bonding arrangement 36 by x-rays 34, whether all the solderbumps 24 are wetting the contact surface 20. If such wetting does nottake place, there are abrupt transitions in the intensity variation 32of the x-rays 34, as shown in FIG. 1. If no such abrupt transitions arepresent, i.e., if characteristic 38 includes a continuous transitionalregion 44 for each solder bump 24, it can be assumed that flawlesselectrical contact has been established between component 14 and carriersubstrate 10.

According to the number of components 24 to be examined, seen in planview—i.e., as depicted in FIGS. 1 and 2, viewed from above—the preparedradiograph will show a flat intensity distribution of the x-rays 34 foreach of the solder bumps 24. Since the solder bumps 24 are realized assubstantially spherical, the intensity distribution for each solder bump24 is radial in shape, the regions 44 between corresponding radiirunning about a central point of the solder bump 24 that ischaracterized by the minimum 42 of the intensity 32.

An inspection of the bonding arrangement 36 can optionally be performedby comparing a radiograph of the not-yet-soldered connection accordingto FIG. 1 with a radiograph of the soldered connection according to FIG.2, using as the evaluative criterion the difference between thediscontinuities between minima and maxima in the intensity variation 32and the then continuous transitional regions 44 between the minima 42and the maxima 40. The analysis of the radiographs can be performedeither manually or automatically in a suitable manner, by imageprocessing.

FIG. 3 shows a further embodiment of an already-soldered bondingarrangement 36. No solder stop mask has been used in this case, and thesolder from solder bump 24 is therefore able to flow across contactsurface 20 or the surface of printed circuit trace 18 having contactsurface 20. Due to the good wettability of contact surface 20, thesolder flows only in the direction of printed circuit trace 18, so thatthere is no flow of solder at the terminus 46 of printed circuit trace18, shown on the left here. According to further exemplary embodiments,the contact point 18 can also be realized so that an even flow of soldercan occur in all directions of the bonding plane.

In accordance with the again-depicted examination of the connection onthe basis of the intensity variation 32 of the x-rays 34, it is clearthat there is a continuous transition between the minimum 42 and themaximum 40 of the intensity 32 of the x-rays 34 in the region of flow ofthe solder. If this continuous transitional region 44 is not found onanalysis, but instead there is an abrupt transition between the minimum42 and the maximum 40, it can be concluded that the solder has notwetted the contact surface 20 to the desired extent.

A bonding arrangement 36 according to the prior art is shown in FIG. 4.Here, the ratio between a diameter d₁ of opening 28 in solder stop mask26 and the diameter d₂ of solder bump 24 is almost unity, i.e., theratio of the diameters d₁:d₂ is 1:1, and thus there is essentially nodeformation of the solder bumps 24 in the direction of the bondingplane, so that a two-dimensional x-ray examination performed here leadsto an abrupt transition between the minimum 42 and the maximum 40 of theintensity variation 32 of the x-rays 34. Thus, although the presence ofan electrically conductive connection across a solder bump 24 can bedetected, it is not clear whether adequate wetting of the contactsurface 20 has actually taken place.

FIG. 5 shows a further bonding arrangement 36 in another exemplaryembodiment. The same parts as in the previous figures have been providedwith the same reference numerals and will not be described again.

FIG. 5 depicts two solder bumps 24, of which, the one shown on the leftwetted the pad properly after component 14 was soldered to carriersubstrate 10, whereas the solder bump shown on the right by comparisondid not properly wet pad 18. The deformation of solder bump 24 thatoccurs according to the present invention during soldering isaccomplished in that a solder stop mask 26 is spaced with respect to thepad 18 in such a way that side edge faces 50 of pad 18, i.e., edge faces50 that extend essentially perpendicularly to the bonding plane, areco-wetted by solder bump 24. The wetting of edge faces 50 of pad 18 isreadily possible because, inter alia, the material of the solder bump 24is converted to the molten state during soldering, so that—due to thegood wettability of the material of pad 18, which is made, for example,of gold, aluminum, platinum or the like—the edge faces 50 are co-wettedwhen a residual space between solder stop mask 26 and pad 18 becomesfilled with solder. This spacing between solder stop mask 26 and pad 18enables solder bump 24 to undergo during soldering a set deformationthat can be analyzed by an x-ray method, as explained furtherhereinbelow.

By comparison, solder bump 24 shown on the right has not properly wettedpad 18. The space between solder stop mask 26 and pad 18 is not filledwith the material of solder bump 24, and thus the edge faces 50 of pad18 are not wetted. This can occur, for example, due to contamination ofpad 18 that detracts from its intrinsically good wettability.

In order to check for the proper wetting of pad 18 by solder bumps 24,the layer of bonding arrangement 36 denoted by S in FIG. 5 is examinedby a three-dimensional x-ray technique and is visualized in a radiographschematically indicated in FIG. 6. Layer resolutions of about 30 to 100μm can be achieved with the available 3D x-ray technology. The pads 18,which are deposited on the carrier substrate 18, for example, by screenprinting or another suitable method, usually have a layer thickness ofabout 50 μm. Thus, 3D x-ray technology can be used to extract the layerS containing pads 18 from bonding arrangement 36. Visualization of thislayer S in the radiograph results in the image indicated schematicallyin FIG. 6. In this case, in which pad 18 has been properly wetted, thematerial of solder bump 24 that is within layer S is visible as a ring52 surrounding pad 18. In the image indicated schematically in FIG. 6,however, because the edges 50 of pad 18 have not been wetted, none ofthe material of solder bump 24 in layer S is deformed, and thus no suchmaterial can be seen on the radiograph. Again, on analysis of theradiographs, if a ring 52 is present around pad 18, it can be assumedthat proper wetting of the pads 18 has taken place.

FIG. 7 illustrates a two-dimensional x-ray analysis of the bondingarrangement 36. The depiction of bonding arrangement 36 in FIG. 7corresponds to the bonding arrangement 36 shown in FIG. 5. Correspondingto the wetting of the edges 50 of pads 18, a distribution of thematerial of solder bumps 24 occurs that can be illustrated in atwo-dimensional visualization. In the left-hand diagram of FIG. 7 properwetting of the edges 50 has occurred, resulting in a distribution of thesolder material from solder bumps 24 that corresponds to the intensitycurve 32 shown, a saddle shape being produced in this case. If properwetting of the edges 50 does not occur—as in the right-hand diagram ofFIG. 7—the distribution of the material of solder bump 24 is such thatmuch less solder is present in its marginal areas 53 than at the center55. This results in the x-ray intensity curve 32 shown at the bottom, inwhich this saddle shape does not appear. Observation of a saddle shape51 in the intensity curve 32 is therefore a criterion for proper wettingof the pad 18.

FIG. 8 is the connection diagram of a printed circuit board with n x mpads 18. n and m can be equal to 15, for example. To bring about a setdeformation of the solder bumps during soldering as a result of thewetting of pads 18, pads 18 can have a defined shape viewed in plan.

FIGS. 9g-i are a plan view of various pads 18 depicted on a greatlyenlarged scale in order to illustrate some of the possible definedshapes for the pads 18. The defined shaping of the pads can, forexample, be effected by the realization of a solder stop mask on aprinted circuit trace , in which case a mask opening of the solder stopmask then produces the shape of the pad 18. A further possibility is todeposit the pads 18 themselves on the carrier substrate 10 in theappropriate shape. It is crucial that the geometry of the pads 18deviate from a circular shape that substantially matches the round shapeof the solder bumps, so that upon the wetting of the pads 18 the solderbumps flow according to the geometry of the pads 18 and assume theirshape. This results in an intended deformation of the solder bumps 24.As is apparent from the selection of possibilities shown, the pad 18can, for example, comprise lands projecting from a round shape, as inFIGS. 9a and 9 b; it can be triangular, as in FIG. 9c; it can comprise anose arising from a circular shape, as in FIG. 9d, and oppositelydisposed noses arising from a circular shape, as in FIG. 9e; it can beteardrop-shaped, as in FIG. 9f; oval, as in FIG. 9g; square, as in FIG.9h; and round with one land, as in FIG. 9i. In these cases, all the pads18 to be contacted can have the same geometrical shape or mixed shapes,that is, pads 18 of one printed circuit board can have differentgeometrical shapes. It is advantageous, however, if all the pads on oneprinted circuit board that are to be contacted have the same geometricalshape.

FIG. 10 is a schematic detail of a two-dimensional radiograph that canbe used to check for the proper wetting of pads 18 by solder bumps 24.Here, for example, four solder bumps 24 can be recognized (the filmreproduces further printed circuit trace s and through platings thatwill not be discussed here), of which the two solder bumps 24 shown atthe top have a substantially circular shape, whereas the two solderbumps 24 shown at the bottom have a substantially oval shape. It isclear from this film that based on their oval shape, the solder bumps 24have properly wetted the pads 18, which previously had precisely thisoval shape. The solder bumps 24 shown at the top in FIG. 10 haveretained their original shape as essentially round unsoldered solderbumps 24 and have not properly wetted the pads 18, which are also ovalhere; a defective, cold solder joint can therefore be assumed. Thesetwo-dimensional radiographs, which are relatively easy to prepare forthe comparison, can therefore be used to perform a nondestructive,unambiguous and reliable check for proper bonding, subject to advancepreparation of the pads 18 by the appropriate shaping thereof (examplesshown in FIGS. 9a to 9 i).

What is claimed is:
 1. A method for connecting at least one electroniccomponent to a carrier substrate, comprising the steps of: electricallyconductively connecting at least one pad of the at least one electroniccomponent to at least one pad of the carrier substrate; depositing asolder bump on one of the at least one pad of the at least oneelectronic component and the at least one pad of the carrier substrate;alignedly mating the at least one electronic component with the carriersubstrate; soldering the solder bump to wet contact surfaces of the atleast one electronic component and the carrier substrate; deforming thesolder bump within a contacting plane during soldering so that a degreeof deformation is achieved that permits an analysis of the degree ofdeformation by a radiograph of the contact surfaces; and evaluating acontinuous intensity distribution of the radiograph along a line.
 2. Themethod according to claim 1, wherein: during the step of soldering thesolder bump is distributed so that a thickness of a soldering materialdecreases continuously toward a margin.
 3. The method according to claim1, further comprising the step of: determining the degree of deformationof the solder bump by a solder stop mask, the solder stop maskencompassing the at least one pad of the carrier substrate, the solderbump being fitted into the at least one pad of the carrier substrate. 4.The method according to claim 1, further comprising the step of:determining the degree of deformation of the solder bump by a size ratioof a first diameter of masking openings in a solder stop mask to asecond diameter of the solder bump.
 5. The method according to claim 1,further comprising the step of: intentionally regionally wetting printedcircuit traces to cause the deformation of the solder bump, the printedcircuit traces including the at least one pad of the carrier substrate.6. The method according to claim 1, further comprising the step of:intentionally wetting edge surfaces of the at least one pad of thecarrier substrate to cause the deformation of the solder bump.
 7. Themethod according to claim 1, wherein: the deformation of the solder bumpis effected by a deliberate wetting of the at least one pad of thecarrier substrate, the at least one pad of the carrier substratedeviating from a circular shape.
 8. The method according to claim 1,further comprising the step of: using a flip-chip technique to form theconnection between the at least one pad of the at least one electroniccomponent and the at least one pad of the carrier substrate.
 9. Themethod according to claim 1, further comprising the step of: using aball grid array technique to form the connection between the at leastone pad of the at least one electronic component and the carriersubstrate.
 10. The method according to claim 1, wherein the evaluatingstep includes the substep of identifying abrupt transitions.
 11. Themethod according to claim 1, wherein the evaluating step includes thesubstep of determining wetting of vertical sidewalls of the at least onepad.
 12. A method for examining a connection between an electroniccomponent and a carrier substrate, pads of the electronic componentbeing connected to assigned pads of the carrier substrate via at leastone solder bump, comprising the steps of: after connection of theelectronic component to the carrier substrate, exposing a bondingarrangement to x-rays directed perpendicularly to a contacting plane;making a radiograph on a side of the bonding arrangement facing awayfrom an x-ray source; and analyzing an intensity variation of the x-raysin a transitional region from a solder bump to a region surrounding thesolder bump, the solder bump being deformed during soldering so that oneof a continuous transition of the intensity variation from a minimumintensity to a maximum intensity and a set deformation of the solderbump is measurable when proper wetting of the assigned pads has takenplace.
 13. The method according to claim 12, further comprising the stepof: preparing and analyzing a two-dimensional radiograph of the bondingarrangement.
 14. The method according to claim 12, further comprisingthe step of: preparing and analyzing a three-dimensional radiograph ofthe bonding arrangement in a region of a layer, the layer lying in aplane with at least one pad of the carrier substrate.